The present invention relates to an ending point detecting method and a drift correcting method for correcting an opaque defect of a photomask using an atomic force microscope technique.
A fine processing technique in a nanometer order has been required in order to advance and make high integration of functions, and a processing technique such as a partial anodizing and oxidizing and a fine scratch processing using a scanning probe microscope (SPM) has been famously researched and developed. Recently, a practical processing device has been required to form an accurate shape and have high accurate processing, in addition to pursuit the fine processing property.
An example of a recent device based on an atomic force microscope (AFM), which is required to form an accurate shape and have high accurate processing, is a device for correcting a pattern opaque defect of a photomask (see, for example, Y. Morikawa, H. Kokubo, M. Nishiguchi, N. Hayashi, R. White, R. Bozak, and L. Terrill, Proc. Of SPIE 5130 520-527 (2003). When the opaque defect of a photomask is corrected using an atomic force microscope, a probe of an atomic force microscope harder than a material to be processed (a material having an opaque defect) is used. When observing, the material is imaged having an ordinary low load contact mode or intermittent contact mode of the atomic force microscope so as to recognize a defect portion. Further, when processing, the hard probe is fixed to the same height as the surface of a glass substrate having a high load contact mode or by cutting feedback, and an opaque defect portion on the glass surface is scanned so as to be physically eliminated and processed.
In a case of a focused ion beam defect conventionally used as a device for correcting a fine defect of a photomask, an isolated defect is hardly observed and processed due to charging-up. In such the case, the atomic force microscope can be used for correcting an opaque defect of a photomask and has been recently used in a photomask production field. As a mask is an original edition at the time of wafer transfer, if processing accuracy of a corrected portion is not enough or there is an over etch or grinding remainder, transfer property of the photomask is bad-influenced so as to cause a device defect to all of the transferred wafers. Therefore, a processing to form an accurate shape and have high accuracy is needed by the mechanical eliminating and processing technique using an atomic force microscope.
In a conventional method for correcting an opaque defect of a photomask using an atomic force microscope, a processing is performed by: observing an area including an opaque defect so as to determine an area to be processed (an opaque defect area); and eliminating the area so as not to grind a glass by grinding too much. This processing is performed by: separately and alternately observing to acquire height information; making a processing ending point when reaching an area on a glass surface; and eliminating and processing only a grinding remainder portion next time except the processing ending point. This processing is repeated so as to reduce an over etch or grinding remainder as much as possible. That is, in the conventional method for correcting a pattern opaque defect of a photomask using an atomic force microscope, scanning for processing and scanning for observing are respectively performed in general. In both scanning, only going scanning is performed in order not to deviate an image and a processing position as illustrated in FIG. 2A, and returning scanning is performed while pulling up a probe to the height in order not to contact to the pattern so as to move to a start point of a next scanning as illustrated in FIG. 2B. Therefore, when an opaque defect is corrected by repeating processing and observation many times, much times are necessary for total correcting, so that throughput is decreased.
Further, when a drift is cased during a processing, a processing position is deviated from a desired position. So, a normal pattern is ground or a glass substrate is over-etched so that the optical property is reduced after correcting. Therefore, reducing a drift is an important technique in order to perform a high accuracy processing. However, in the conventional technique, a drift is corrected by: moving a probe to an observation start point of a drift marker during a processing so as to observe; comparing XY information of the marker before processing with that after observing; calculating a drift amount; and adding an offset of the drift amount to an area to be processed next time. In this case, the probe is moved to a portion which will be a drift marker of a processing area after processing, so that it takes time.
The present invention solves the above-described problems, and an objective of the present invention is to realize a high accuracy processing not having an over etch and grinding remainder while increasing throughput when a defect of a mask is corrected using an atomic force microscope technique.